2.2.43
DIVERSITY OF RALSTONIA SOLANACEARUM IN EGGPLANT AND ITS RHIZOSPHERE SOIL

M HORITA1, K TSUCHIYA1, Y IWAMOTO2 and J YAMAGUCHI3

1National Institute of Agrobiological Resources, Kannondai 2-1-2, Tsukuba, Ibaraki 305-0856, Japan; 2Osaka Prefectural Agricultural and Forestry Research Centre, Habikino, Osaka 583-0862, Japan; 3Saga Prefectural Agricultural Research Centre, Kawasoe, Saga 840-2205, Japan

Background and objectives

Bacterial wilt disease of solanaceous crops caused by Ralstonia solanacearum (Rs) is very important problem in Japan and effective use is usually made of resistant rootstock cultivar. Recently, the occurrence of a new pathogenicity group frequently has broken down the resistance. To control this disease, we assessed the population dynamics of Rs in or around host plant (eggplant), and the genetic diversity of Rs by using rep-PCR [1].

Results and conclusions
Eggplant (grafting of susceptible cultivar Senryo 2-go on resistant rootstock 'Karehen') was cultivated during summer (July to September) in an artificially infested field. Eleven weeks after planting, half of the plants were wilted and dead. Both wilted and healthy plants with soil were then collected and Rs was isolated. The Rs population in both rhizoshere soil was over 104 ;cfu/g dry weight and each of 40 isolates showed several polymorphic patterns by rep-PCR. In wilted plants, Rs was detected over 106 ;cfu/g fresh matter (FM) from roots and stems near the grafting site. The 80 stem isolates showed only one polymorphic pattern, which was very similar to that of soil isolates. In healthy plants, Rs was detected only from roots under 3X102 ;cfu/g FM and browning in stem at the rootstock was observed. Each strain which differed in isolation site and/or polymorphic pattern is now being tested for their pathogenicity.

Reference
1. Horita M, Tsuchiya K, Nunome T, 1997. Abstracts of 2nd International Bacterial Wilt Symposium, p. 23.